The present invention relates to a method for uniformly heating a glass stream flowing in the feeder of a glass melting, furnace, wherein power or energy is supplied through electrodes immersed in the glass melt, and wherein the temperature of the glass stream is continuously detected, as well as to a system for carrying out such method and including electrodes which pass on opposite sides through the wall of the feeder in pairs and which are conductively connected to windings of transformers, and further comprising temperature detecting elements for detecting the temperature of the glass stream at least in the inlet region of the feeder.
It is known to connect in groups, the electrodes passing horizontally through the sidewall of the duct, which groups may be termed heating zones. In this system, the electrodes are connected in parallel circuit configuration to the secondary portion of a transformer, with the electrodes of one heating zone being controlled in combination through a voltage regulator (thyristor or variable-ratio transformer). In this system, the electrodes on the one side of the feeder are electrically connected to the one output side of the secondary portion of the transformer, while those of the other side are connected to the opposite side of the transformer which may be a variable-ratio transformer, as known. Systems of this type are described, for example, in U.S. Pat. No. 4,029,488, and suffer from the drawback, however, that identical voltages exist between the pairs of electrodes of each heating zone, although different resistance are present across the glass stream such that different degrees of power consumption exist therein. Accordingly, it is not possible to compensate in an optimum manner for temperature non-homogeneities in the glass stream.
It is further known from German laid-open application No. 2,626,788 to effect the uniform heating of molten glass by connecting the pairs of electrodes to power sources in the form of transformers, the primary windings of which are series-connected and with each secondary winding conductively connected to a pair of electrodes.
Actually, this system allows the control of the output power between each electrode pair to equal values by combining the outputs of all pairs of electrodes however, it is a disadvantage of this system that control of the output of separate electrode pairs is not feasible so that the compensation of temperature variations can be effected only to a limited extent. Accordingly, particularly in the case when control should be effected because of a spontaneous undesirable temperature variation, an over-correction takes place which results in impairment of the operation.
In view of the fact that temperature measuring cells or detectors in most instances respond only with a time delay, a satisfactory solution to the existing problems is not even possible with the use of such elements and with the employment of the conventional manually variable transformers.
It is a further disadvantage of the conventional control systems or feeder heating systems that, due to the direct heating by means of electrodes, the thermal homogeneity must necessarily be imperfect, because power concentration at the tip ends of the electrodes occurs and the current still flows through regions of higher temperature because of the lower resistances existing therein. Thus, the cooler portions can be heated only insufficiently, and the desired temperature homogeneity only can be obtained imperfectly because of the deficiencies of such systems.